Add a failure integration test case that requires mimic

Add test that requires mimic - inject server build failure, and test that the server fails to build.

This should pass on master, and should also still pass on #660 

The `time.sleep` is unfortunate, but since reads are consistency one....  :|  I did check that not injecting the error results in the test hanging until it fails.

I would also like to check that pending is 1 when we get the server creation response back, but unfortunately there is a bug associated with that (currently in the process of filing)

This takes advantage of [this particular](https://github.com/rackerlabs/mimic/blob/master/mimic/canned_responses/nova.py#L113) error injection feature in mimic.  The mechanism may change soon in a later version of mimic.
I believe on the dev vm, no time, because there's just the single cass node.  I mostly added this for future when we might be running against a cluster for preprod?